A typical fuel cell system includes a power section in which one or more fuel cells generate electrical power. A fuel cell is an energy conversion device that converts hydrogen and oxygen into water, producing electricity and heat in the process. Each fuel cell unit may include a proton exchange membrane (PEM) at the center with gas diffusion layers on either side of the PEM. Anode and cathode catalyst layers are respectively positioned at the inside of the gas diffusion layers. This unit is referred to as a membrane electrode assembly (MEA). Separator plates or flow field plates are respectively positioned on the outside of the gas diffusion layers of the membrane electrode assembly. This type of fuel cell is often referred to as a PEM fuel cell.
In a fuel cell there is a desire for the polymer of the PEM to have a low equivalent weight, thus having many sites for proton exchange. However, traditionally the low equivalent weight polymers do not have sufficient physical properties to make them useful in membrane materials.
It is a common practice in the industry to use uncrosslinked sulfonated polymers in PEMs, such as those sold under the trade designation “NAFION” (DuPont Chemicals, Inc., Wilmington, Del.), which is made of copolymers of tetrafluoroethylene and perfluorovinylether sulfonic acid. However, these commercially available PEMs are not entirely satisfactory in meeting the performance demands of fuel cells. For example, NAFION membranes with lower equivalent weight can achieve lower electrical resistance, but these membranes are also structurally weaker.